Surgical navigation systems and processes for unicompartmental knee arthroplasty

ABSTRACT

Systems and processes for tracking anatomy, instrumentation, trial implants, implants, and references, and rendering images and data related to them in connection with surgical operations, for example unicompartmental knee arthroplasties (“UKA”). These systems and processes are accomplished by using a computer to intraoperatively obtain images of body parts and to register, navigate, and track surgical instruments.

RELATED APPLICATION DATA

This document claims the benefit of U.S. Ser. No. 60/271,818, filed Feb.27, 2001 entitled “Image Guided System for Arthroplasty” and U.S. Ser.No. 60/355,899, filed Feb. 11, 2002 entitled “Surgical NavigationSystems and Processes,” which documents are incorporated herein by thisreference.

FIELD OF THE INVENTION

This invention generally relates to unicompartmental knee arthroplastysurgical operations using systems and processes for tracking anatomy,implements, instrumentation, trial implants, implant components andvirtual constructs or references, and rendering images and data relatedto them. Anatomical structures and such items may be attached to orotherwise associated with fiducial functionality, and constructs may beregistered in position using fiducial functionality whose position andorientation can be sensed and tracked by systems and according toprocesses of the present invention in three dimensions in order toperform unicompartmental knee arthroplasty. Such structures, items andconstructs can be rendered onscreen properly positioned and orientedrelative to each other using associated image files, data files, imageinput, other sensory input, based on the tracking. Such systems andprocesses, among other things, allow surgeons to navigate and performunicompartmental knee arthroplasty using images that reveal interiorportions of the body combined with computer generated or transmittedimages that show surgical implements, instruments, trials, implants,and/or other devices located and oriented properly relative to the bodypart. Such systems and processes allow, among other things, moreaccurate and effective resection of bone, placement and assessment oftrial implants and joint performance, and placement and assessment ofperformance of actual implants and joint performance.

BACKGROUND

Knee arthroplasty is a surgical procedure in which the articularsurfaces of the femur, tibia and patella are cut away and replaced bymetal and/or plastic prosthetic components. The goals of kneearthroplasty include resurfacing the bones in the knee joint andrepositioning the joint center on the mechanical axis of the leg. Kneearthroplasty is generally recommended for patients with severe knee painand disability caused by damage to cartilage from rheumatoid arthritis,osteoarthritis or trauma. It can be highly successful in relieving painand restoring joint function.

More than 95% of knee arthroplasties performed in the United States aretricompartmental knee arthroplasties (“TKA”), which involves thereplacement of all the articular surfaces of the knee joint. TKA isperformed when arthritis or trauma has affected two or more of the threecompartments of the knee: medial compartment (toward the body's centralaxis), lateral compartment (away from the body's central axis), andpatello-femoral compartment (toward the front of the knee).

The remaining knee arthroplasties are unicompartmental kneearthroplasties (“UKA”). UKA involves the replacement of the articularsurfaces of only one knee compartment, usually the medial compartment.UKA is an attractive surgical treatment for patients with arthritis inonly one compartment and with a healthy patella.

UKA has several advantages over TKA. UKA allows the preservation of bothcruciate ligaments, while the anterior cruciate ligament is usuallyremoved in TKA. Preservation of the ligaments provides greater stabilityto the joint after surgery. UKA also allows for preservation of morebone stock at the joint, which will be beneficial if revision componentsmust be placed. Finally, UKA is less invasive than TKA because UKArequires smaller resections and components.

In spite of these advantages, there continue to be problems in UKAperformance. A leading cause of wear and revision in prosthetics such asknee implants, hip implants and shoulder implants is less than optimumimplant alignment. In a UKA, for example, current instrument design forresection of bone limits the alignment of the femoral and tibialresections to average values for varus/valgus flexion/extension, andexternal/internal rotation. Additionally, surgeons often use visuallandmarks or “rules of thumb” for alignment which can be misleading dueto anatomical variability. Intramedullary referencing instruments alsoviolate the femoral and tibial canal. This intrusion increases the riskof fat embolism and unnecessary blood loss in the patient. Surgeons alsorely on instrumentation to predict the appropriate implant size for thefemur and tibia instead of the ability to intraoperatively template theappropriate size of the implants for optimal performance. Anotherchallenge for surgeons is soft tissue or ligament balancing after thebone resections have been made. Releasing some of the soft tissue pointscan change the balance of the knee; however, the multiple options can beconfusing for many surgeons. Although much of the bone stock remainsafter UKA, if a revision is necessary, many of the visual landmarks areno longer present, making alignment and restoration of the joint linedifficult.

SUMMARY

The present invention is applicable not only for knee repair,reconstruction or replacement surgery, but also repair, reconstructionor replacement surgery in connection with any other joint of the body aswell as any other surgical or other operation where it is useful totrack position and orientation of body parts, non-body components and/orvirtual references such as rotational axes, and to display and outputdata regarding positioning and orientation of them relative to eachother for use in navigation and performance of the operation.

Systems and processes according to one embodiment of the presentinvention use position and/or orientation tracking sensors such asinfrared sensors acting stereoscopically or otherwise to track positionsof body parts, surgery-related items such as implements,instrumentation, trial prosthetics, prosthetic components, and virtualconstructs or references such as rotational axes which have beencalculated and stored based on designation of bone landmarks. Processingcapability such as any desired form of computer functionality, whetherstandalone, networked, or otherwise, takes into account the position andorientation information as to various items in the position sensingfield (which may correspond generally or specifically to all or portionsor more than all of the surgical field) based on sensed position andorientation of their associated fiducials or based on stored positionand/or orientation information. The processing functionality correlatesthis position and orientation information for each object with storedinformation regarding the items, such as a computerized fluoroscopicimaged file of a femur or tibia, a wire frame data file for rendering arepresentation of an instrumentation component, trial prosthesis oractual prosthesis, or a computer generated file relating to a rotationalaxis or other virtual construct or reference. The processingfunctionality then displays position and orientation of these objects ona screen or monitor, or otherwise. Thus, systems and processes accordingto one embodiment of the invention can display and otherwise outputuseful data relating to predicted or actual position and orientation ofbody parts, surgically related items, implants, and virtual constructsfor use in navigation, assessment, and otherwise performing surgery orother operations.

As one example, images such as fluoroscopy images showing internalaspects of the femur and tibia can be displayed on the monitor incombination with actual or predicted shape, position and orientation ofsurgical implements, instrumentation components, trial implants, actualprosthetic components, and rotational axes in order to allow the surgeonto properly position and assess performance of various aspects of theknee joint being repaired, reconstructed or replaced. The surgeon maynavigate tools, instrumentation, trial prostheses, actual prostheses andother items relative to the femur and tibia in order to perform UKA'smore accurately, efficiently, and with better alignment and stability.

Systems and processes according to the present invention can also usethe position tracking information and, if desired, data relating toshape and configuration of surgical related items and virtual constructsor references in order to produce numerical data which may be used withor without graphic imaging to perform tasks such as assessingperformance of trial prosthetics statically and throughout a range ofmotion, appropriately modifying tissue such as ligaments to improve suchperformance and similarly assessing performance of actual prostheticcomponents which have been placed in the patient for alignment andstability.

Systems and processes according to the present invention can alsogenerate data based on position tracking and, if desired, otherinformation to provide cues on screen, aurally or as otherwise desiredto assist in the surgery such as suggesting certain bone modificationsteps or measures which may be taken to release certain ligaments orportions of them based on performance of components as sensed by systemsand processes according to the present invention.

According to a preferred embodiment of systems and processes accordingto the present invention, at least the following steps are involved:

1. Obtain appropriate images such as fluoroscopy images of appropriatebody parts such as femur and tibia, the imager being tracked in positionvia an associated fiducial whose position and orientation is tracked byposition/orientation sensors such as stereoscopic infrared (active orpassive) sensors according to the present invention.

2. Register tools, instrumentation, trial components, prostheticcomponents, and other items to be used in surgery, each of whichcorresponds to a fiducial whose position and orientation can be trackedby the position/orientation sensors.

3. Locating and registering body structure such as designating points onthe femur and tibia using a probe associated with a fiducial in order toprovide the processing functionality information relating to the bodypart such as rotational axes.

4. Navigating and positioning instrumentation such as cuttinginstrumentation in order to modify bone, at least partially using imagesgenerated by the processing functionality corresponding to what is beingtracked and/or has been tracked, and/or is predicted by the system, andthereby resecting bone effectively, efficiently and accurately.

5. Navigating and positioning trial components such as femoralcomponents and tibial components, some or all of which may be installedusing impactors with a fiducial and, if desired, at the appropriate timediscontinuing tracking the position and orientation of the trialcomponent using the impactor fiducial and starting to track thatposition and orientation using the body part fiducial on which thecomponent is installed.

6. Assessing alignment and stability of the trial components and joint,both statically and dynamically as desired, using images of the bodyparts in combination with images of the trial components whileconducting appropriate rotation, anterior-posterior drawer andflexion/extension tests and automatically storing and calculatingresults to present data or information which allows the surgeon toassess alignment and stability.

7. Releasing tissue such as ligaments if necessary and adjusting trialcomponents as desired for acceptable alignment and stability.

8. Installing implant components whose positions may be tracked at firstvia fiducials associated with impactors for the components and thentracked via fiducials on the body parts in which the components areinstalled.

9. Assessing alignment and stability of the implant components and jointby use of some or all tests mentioned above and/or other tests asdesired, releasing tissue if desired, adjusting if desired, andotherwise verifying acceptable alignment, stability and performance ofthe prosthesis, both statically and dynamically.

This process, or processes including it or some of it may be used in anytotal or partial joint repair, reconstruction or replacement, includingknees, hips, shoulders, elbows, ankles and any other desired joint inthe body.

Systems and processes according to the present invention representsignificant improvement over other previous systems and processes. Forinstance, systems which use CT and MRI data generally require theplacement of reference frames pre-operatively which can lead toinfection at the pin site. The resulting 3D images must then beregistered, or calibrated, to the patient anatomy intraoperatively.Current registration methods are less accurate than the fluoroscopicsystem. These imaging modalities are also more expensive. Some“imageless” systems, or non-imaging systems, require digitizing a largenumber of points to define the complex anatomical geometries of the kneeat each desired site. This can be very time intensive resulting inlonger operating room time. Other imageless systems determine themechanical axis of the knee by performing an intraoperative kinematicmotion to determine the center of rotation at the hip, knee, and ankle.This requires placement of reference frames at the iliac crest of thepelvis and in or on the ankle. This calculation is also time consumingat the system must find multiple points in different planes in order tofind the center of rotation. This is also problematic in patients withpathologic conditions. Ligaments and soft tissues in the arthriticpatient are not normal and thus will give a center of rotation that isnot desirable for normal knees. Robotic systems require expensive CT orMRI scans and also require pre-operative placement of reference frames,usually the day before surgery. These systems are also much slower,almost doubling operating room time and expense.

None of these systems can effectively track femoral and/or tibial trialsduring a range of motion and calculate the relative positions of thearticular surfaces, among other things. Also, none of them currentlymake suggestions on ligament balancing, display ligament balancingtechniques, or surgical techniques. Additionally, none of these systemscurrently track the patella.

An object of certain aspects of the present invention is to use computerprocessing functionality in combination with imaging and position and/ororientation tracking sensors to present to the surgeon during surgicaloperations visual and data information useful to navigate, track and/orposition implements, instrumentation, trial components, prostheticcomponents and other items and virtual constructs relative to the humanbody in order to improve performance of a repaired, replaced orreconstructed knee joint.

Another object of certain aspects of the present invention is to usecomputer processing functionality in combination with imaging andposition and/or orientation tracking sensors to present to the surgeonduring surgical operations visual and data information useful to assessperformance of a knee and certain items positioned therein, includingcomponents such as trial components and prosthetic components, forstability, alignment and other factors, and to adjust tissue and bodyand non-body structure in order to improve such performance of arepaired, reconstructed or replaced knee joint.

Another object of certain aspects of the present invention is to usecomputer processing functionality in combination with imaging andposition and/or orientation tracking sensors to present to the surgeonduring surgical operations visual and data information useful to showany or all of predicted position and movement of implements,instrumentation, trial components, prosthetic components and other itemsand virtual constructs relative to the human body in order to selectappropriate components, resect bone accurately, effectively andefficiently, and thereby improve performance of a repaired, replaced orreconstructed knee joint.

Other objects, features and advantages of the present invention areapparent with respect to the remainder of this document.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a particular embodiment of systems andprocesses according to the present invention.

FIG. 2 is a view of a knee prepared for surgery, including a femur and atibia to which fiducials according to one embodiment of the presentinvention have been attached.

FIG. 3 is a view of a portion of a leg prepared for surgery according tothe present invention with a C-arm for obtaining fluoroscopic imagesassociated with a fiducial according to one embodiment of the presentinvention.

FIG. 4 is a fluoroscopic image of free space rendered on a monitoraccording to one embodiment of the present invention.

FIG. 5 is a fluoroscopic image of femoral head obtained and renderedaccording one embodiment of the present invention.

FIG. 6 is a fluoroscopic image of a knee obtained and rendered accordingto one embodiment of the present invention.

FIG. 7 is a fluoroscopic image of a tibia distal end obtained andrendered according to one embodiment of the present invention.

FIG. 8 is a fluoroscopic image of a lateral view of a knee obtained andrendered according to one embodiment of the present invention,

FIG. 9 is a fluoroscopic image of a lateral view of a knee obtained andrendered according to one embodiment of the present invention.

FIG. 10 is a fluoroscopic image of a lateral view of a tibia distal endobtained and rendered according to one embodiment of the presentinvention.

FIG. 11 shows a probe according to one embodiment of the presentinvention being used to register a surgically related component fortracking according to one embodiment of the present invention.

FIG. 12 shows a probe according to one embodiment of the presentinvention being used to register a cutting block for tracking accordingto one embodiment of the present invention.

FIG. 13 shows a probe according to one embodiment of the presentinvention being used to register a tibial cutting block for trackingaccording to one embodiment of the present invention.

FIG. 14 shows a probe according to one embodiment of the presentinvention being used to register an alignment guide for trackingaccording to one embodiment of the present invention.

FIG. 15 shows a probe according to one embodiment of the presentinvention being used to designate landmarks on bone structure fortracking according to one embodiment of the present invention.

FIG. 16 is another view of a probe according to one embodiment of thepresent invention being used to designate landmarks on bone structurefor tracking according to one embodiment of the present invention.

FIG. 17 is another view of a probe according to one embodiment of thepresent invention being used to designate landmarks on bone structurefor tracking according to one embodiment of the present invention.

FIG. 18 is a screen face produced according to one embodiment of thepresent invention during designation of landmarks to determine a femoralmechanical axis.

FIG. 19 is a view produced according to one embodiment of the presentinvention during designation of landmarks to determine a tibialmechanical axis.

FIG. 20 is a screen face produced according to one embodiment of thepresent invention during designation of landmarks to determine anepicondylar axis.

FIG. 21 is a screen face produced according to one embodiment of thepresent invention during designation of landmarks to determine ananterior-posterior axis.

FIG. 22 is a screen face produced according to one embodiment of thepresent invention during designation of landmarks to determine aposterior condylar axis.

FIG. 23 is a screen face according to one embodiment of the presentinvention which presents graphic indicia which may be employed to helpdetermine reference locations within bone structure.

FIG. 24 is a screen face according to one embodiment of the presentinvention showing mechanical and other axes which have been establishedaccording to one embodiment of the present invention.

FIG. 25 is another screen face according to one embodiment of thepresent invention showing mechanical and other axes which have beenestablished according to one embodiment of the present invention.

FIG. 26 is another screen face according to one embodiment of thepresent invention showing mechanical and other axes which have beenestablished according to one embodiment of the present invention.

FIG. 27 shows navigation and placement of an extramedullary rodaccording to one embodiment of the present invention.

FIG. 28 is another view showing navigation and placement of anextramedullary rod according to one embodiment of the present invention.

FIG. 29 is a screen face produced according to one embodiment of thepresent invention which assists in navigation and/or placement of anextramedullary rod.

FIG. 30 is another view of a screen face produced according to oneembodiment of the present invention which assists in navigation and/orplacement of an extramedullary rod.

FIG. 31 is a view which shows navigation and placement of an alignmentguide according to one embodiment of the present invention.

FIG. 32 is another view which shows navigation and placement of analignment guide according to one embodiment of the present invention.

FIG. 33 is a view showing placement of an alignment guide according toone embodiment of the present invention.

FIG. 34 is another view showing placement of a cutting block accordingto one embodiment of the present invention.

FIG. 35 is a view showing navigation and placement of the cutting blockof FIG. 45.

FIG. 36 is another view showing navigation and placement of a cuttingblock according to one embodiment of the present invention.

FIG. 37 is a view showing navigation and placement of a tibial cuttingblock according to one embodiment of the present invention.

FIG. 38 is a view showing the UKA femoral and tibial implant components.

FIG. 39 is a view showing the UKA femoral and tibial implant componentsattached at the knee joint.

DETAILED DESCRIPTION

Systems and processes according to a preferred embodiment of the presentinvention use computer capacity, including standalone and/or networked,to store data regarding spatial aspects of surgically related items andvirtual constructs or references including body parts, implements,instrumentation, trial components, prosthetic components and rotationalaxes of body parts. Any or all of these may be physically or virtuallyconnected to or incorporate any desired form of mark, structure,component, or other fiducial or reference device or technique whichallows position and/or orientation of the item to which it is attachedto be sensed and tracked, preferably in three dimensions of translationand three degrees of rotation as well as in time if desired.

In a preferred embodiment, orientation of the elements on a particularfiducial varies from one fiducial to the next so that sensors accordingto the present invention may distinguish between various components towhich the fiducials are attached in order to correlate for display andother purposes data files or images of the components. In a preferredembodiment of the present invention, some fiducials use reflectiveelements and some use active elements, both of which may be tracked bypreferably two, sometimes more infrared sensors whose output may beprocessed in concert to geometrically calculate position and orientationof the item to which the fiducial is attached.

Position/orientation tracking sensors and fiducials need not be confinedto the infrared spectrum. Any electromagnetic, electrostatic, light,sound, radiofrequency or other desired technique may be used.Alternatively, each item such as a surgical implement, instrumentationcomponent, trial component, implant component or other device maycontain its own “active” fiducial such as a microchip with appropriatefield sensing or position/orientation sensing functionality andcommunications link such as spread spectrum RF link, in order to reportposition and orientation of the item. Such active fiducials, or hybridactive/passive fiducials such as transponders can be implanted in thebody parts or in any of the surgically related devices mentioned above,or conveniently located at their surface or otherwise as desired.Fiducials may also take the form of conventional structures such as ascrew driven into a bone, or any other three dimensional item attachedto another item, position and orientation of such three dimensional itemable to be tracked in order to track position and orientation of bodyparts and surgically related items. Hybrid fiducials may be partlypassive, partly active such as inductive components or transponderswhich respond with a certain signal or data set when queried by sensorsaccording to the present invention.

Systems and processes according to a preferred embodiment of the presentinvention employ a computer to calculate and store reference axes ofbody components such as in a UKA, for example, the mechanical axis ofthe femur and tibia. From these axes such systems track the position ofthe instrumentation and osteotomy guides so that bone resections willlocate the implant position optimally, usually aligned with themechanical axis. Furthermore, during trial reduction of the knee, thesystems provide feedback on the balancing of the ligaments in a range ofmotion and under varus/valgus, anterior/posterior and rotary stressesand can suggest or at least provide more accurate information than inthe past about which ligaments the surgeon should release in order toobtain correct balancing, alignment and stability. Systems and processesaccording to the present invention can also suggest modifications toimplant size, positioning, and other techniques to achieve optimalkinematics. Systems and processes according to the present invention canalso include databases of information regarding tasks such as ligamentbalancing, in order to provide suggestions to the surgeon based onperformance of test results as automatically calculated by such systemsand processes.

FIG. 1 is a schematic view showing one embodiment of a system accordingto the present invention and one version of a setting according to thepresent invention in which surgery on a knee, in this case aUnicompartmental Knee Arthroplasty, may be performed. Systems andprocesses according to the present invention can track various bodyparts such as tibia 10 and femur 12 to which fiducials of the sortdescribed above or any other sort may be implanted, attached, orotherwise associated physically, virtually, or otherwise. In theembodiment shown in FIG. 1, fiducials 14 are structural frames some ofwhich contain reflective elements, some of which contain LED activeelements, some of which can contain both, for tracking usingstereoscopic infrared sensors suitable, at least operating in concert,for sensing, storing, processing and/or outputting data relating to(“tracking”) position and orientation of fiducials 14 and thuscomponents such as 10 and 12 to which they are attached or otherwiseassociated. Position sensor 16, as mentioned above, may be any sort ofsensor functionality for sensing position and orientation of fiducials14 and therefore items with which they are associated, according towhatever desired electrical, magnetic, electromagnetic, sound, physical,radio frequency, or other active or passive technique. In the preferredembodiment, position sensor 16 is a pair of infrared sensors disposed onthe order of a meter, sometimes more, sometimes less, apart and whoseoutput can be processed in concert to provide position and orientationinformation regarding fiducials 14.

In the embodiment shown in FIG. 1, computing functionality 18 caninclude processing functionality, memory functionality, input/outputfunctionality whether on a standalone or distributed basis, via anydesired standard, architecture, interface and/or network topology. Inthis embodiment, computing functionality 18 is connected to a monitor onwhich graphics and data may be presented to the surgeon during surgery.The screen preferably has a tactile interface so that the surgeon maypoint and click on screen for tactile screen input in addition to orinstead of, if desired, keyboard and mouse conventional interfaces.Additionally, a foot pedal 20 or other convenient interface may becoupled to functionality 18 as can any other wireless or wirelineinterface to allow the surgeon, nurse or other desired user to controlor direct functionality 18 in order to, among other things, captureposition/orientation information when certain components are oriented oraligned properly. Items 22 such as trial components, instrumentationcomponents may be tracked in position and orientation relative to bodyparts 10 and 12 using fiducials 14.

Computing functionality 18 can process, store and output on monitor 24and otherwise various forms of data which correspond in whole or part tobody parts 10 and 12 and other components for item 22. For example, inthe embodiment shown in FIG. 1, body parts 10 and 12 are shown incross-section or at least various internal aspects of them such as bonecanals and surface structure are shown using fluoroscopic images. Theseimages are obtained using a C-arm attached to a fiducial 14. The bodyparts, for example, tibia 10 and femur 12, also have fiducials attached.When the fluoroscopy images are obtained using the C-arm with fiducial14, a position/orientation sensor 16 “sees” and tracks the position ofthe fluoroscopy head as well as the positions and orientations of thetibia 10 and femur 12. The computer stores the fluoroscopic images withthis position/orientation information, thus correlating position andorientation of the fluoroscopic image relative to the relevant body partor parts. Thus, when the tibia 10 and corresponding fiducial 14 move,the computer automatically and correspondingly senses the new positionof tibia 10 in space and can correspondingly move implements,instruments, references, trials and/or implants on the monitor 24relative to the image of tibia 10. Similarly, the image of the body partcan be moved, both the body part and such items may be moved, or the onscreen image otherwise presented to suit the preferences of the surgeonor others and carry out the imaging that is desired. Similarly, when anitem 22, such as an extramedullary rod, intramedullar rod, or any othertype of rod, that is being tracked moves, its image moves on monitor 24so that the monitor shows the item 22 in proper position and orientationon monitor 24 relative to the femur 12: The rod 22 can thus appear onthe monitor 24 in proper or improper alignment with respect to themechanical axis and other features of the femur 12, as if the surgeonwere able to see into the body in order to navigate and position rod 22properly.

The computer functionality 18 can also store data relating toconfiguration, size and other properties of items 22 such as implements,instrumentation, trial components, implant components and other itemsused in surgery. When those are introduced into the field ofposition/orientation sensor 16, computer functionality 18 can generateand display overlain or in combination with the fluoroscopic images ofthe body parts 10 and 12, computer generated images of implements,instrumentation components, trial components, implant components andother items 22 for navigation, positioning, assessment and other uses.

Additionally, computer functionality 18 can track any point in theposition/orientation sensor 16 field such as by using a designator or aprobe 26. The probe also can contain or be attached to a fiducial 14.The surgeon, nurse, or other user touches the tip of probe 26 to a pointsuch as a landmark on bone structure and actuates the foot pedal 20 orotherwise instructs the computer 18 to note the landmark position. Theposition/orientation sensor 16 “sees” the position and orientation offiducial 14 “knows” where the tip of probe 26 is relative to thatfiducial 14 and thus calculates and stores, and can display on monitor24 whenever desired and in whatever form or fashion or color, the pointor other position designated by probe 26 when the foot pedal 20 is hitor other command is given. Thus, probe 26 can be used to designatelandmarks on bone structure in order to allow the computer 18 to storeand track, relative to movement of the bone fiducial 14, virtual orlogical information such as mechanical axis 28, medial laterial axis 30and anterior/posterior axis 32 of femur 12, tibia 10 and other bodyparts in addition to any other virtual or actual construct or reference.

Systems and processes according to an embodiment of the presentinvention such as the subject of FIGS. 2-36, can use the so-calledFluoroNAV system and software provided by Medtronic Sofamor DanekTechnologies. Such systems or aspects of them are disclosed in U.S. Pat.Nos. 5,383,454; 5,871,445; 6,146,390; 6,165,81; 6,235,038 and 6,236,875,and related (under 35 U.S.C. Section 119 and/or 120) patents, which areall incorporated herein by this reference. Any other desired systems canbe used as mentioned above for imaging, storage of data, tracking ofbody parts and items and for other purposes.

The FluoroNav system requires the use of reference frame type fiducials14 which have four and in some cases five elements tracked by infraredsensors for position/orientation of the fiducials and thus of the bodypart, implement, instrumentation, trial component, implant component, orother device or structure being tracked. Such systems also use at leastone probe 26 which the surgeon can use to select, designate, register,or otherwise make known to the system a point or points on the anatomyor other locations by placing the probe as appropriate and signaling orcommanding the computer to note the location of, for instance, the tipof the probe. The FluoroNav system also tracks position and orientationof a C-arm used to obtain fluoroscopic images of body parts to whichfiducials have been attached for capturing and storage of fluoroscopicimages keyed to position/orientation information as tracked by thesensors 16. Thus, the monitor 24 can render fluoroscopic images of bonesin combination with computer generated images of virtual constructs andreferences together with implements, instrumentation components, trialcomponents, implant components and other items used in connection withsurgery for navigation, resection of bone, assessment and otherpurposes.

FIGS. 2-39 are various views associated with Unicompartmental KneeArthroplasty surgery processes according to one particular embodimentand version of the present invention being carried out with theFluoroNav system referred to above. FIG. 2 shows a human knee in thesurgical field, as well as the corresponding femur and tibia to whichfiducials 14 have been rigidly attached in accordance with thisembodiment of the invention. Attachment of fiducials 14 preferably isaccomplished using structure that withstands vibration of surgical sawsand other phenomenon which occur during surgery without allowing anysubstantial movement of fiducial 14 relative to body part being trackedby the system.

FIG. 3 shows fluoroscopy images being obtained of the body parts withfiducials 14 attached. The fiducial 14 on the fluoroscopy head in thisembodiment is a cylindrically shaped cage which contains LEDs or“active” emitters for tracking by the sensors 16. Fiducials 14 attachedto tibia 10 and femur 12 can also be seen. The fiducial 14 attached tothe femur 12 uses LEDs instead of reflective spheres and is thus active,fed power by the wire seen extending into the bottom of the image.

FIGS. 4-10 are fluoroscopic images shown on monitor 24 obtained withposition and/or orientation information received by, noted and storedwithin computer 18. FIG. 4 is an open field with no body part image, butwhich shows the optical indicia which may be used to normalize the imageobtained using a spherical fluoroscopy wave front with the substantiallyflat surface of the monitor 24. FIG. 5 shows an image of the femur 12head. This image is taken in order to allow the surgeon to designate thecenter of rotation of the femoral head for purposes of establishing themechanical axis and other relevant constructs relating to of the femuraccording to which the prosthetic components will ultimately bepositioned. Such center of rotation can be established by articulatingthe femur within the acetabulum or a prosthesis to capture a number ofsamples of position and orientation information and thus in turn toallow the computer to calculate the average center of rotation. Thecenter of rotation can be established by using the probe and designatinga number of points on the femoral head and thus allowing the computer tocalculate the geometrical center or a center which corresponds to thegeometry of points collected. Additionally, graphical representationssuch as controllably sized circles displayed on the monitor can befitted by the surgeon to the shape of the femoral head on planar imagesusing tactile input on screen to designate the centers according to thatgraphic, such as are represented by the computer as intersection of axesof the circles. Other techniques for determining, calculating orestablishing points or constructs in space, whether or not correspondingto bone structure, can be used in accordance with the present invention.

FIG. 5 shows a fluoroscopic image of the femoral head while FIG. 6 showsan anterior/posterior view of the knee which can be used to designatelandmarks and establish axes or constructs such as the mechanical axisor other rotational axes. FIG. 7 shows the distal end of the tibia andFIG. 8 shows a lateral view of the knee. FIG. 9 shows another lateralview of the knee while FIG. 10 shows a lateral view of the distal end ofthe tibia.

Registration of Surgically Related Items

FIGS. 11-14 show designation or registration of items 22 which will beused in surgery. Registration simply means, however it is accomplished,ensuring that the computer knows which body part, item or constructcorresponds to which fiducial or fiducials, and how the position andorientation of the body part, item or construct is related to theposition and orientation of its corresponding fiducial or a fiducialattached to an impactor or other component which is in turn attached toan item. Such registration or designation can be done before or afterregistering bone or body parts as discussed with respect to FIGS. 4-10.FIG. 11 shows a technician designating with probe 26 an item 22 such asan instrument component to which fiducial 14 is attached. The sensor 16“sees” the position and orientation of the fiducial 14 attached to theitem 22 and also the position and orientation of the fiducial 14attached to the probe 26 whose tip is touching a landmark of the item22. The technician designates onscreen or otherwise the identificationof the item and then activates the foot pedal or otherwise instructs thecomputer to correlate the data corresponding to such identification,such as data needed to represent a particular cutting block componentfor a particular knee implant product, with the particularly shapedfiducial 14 attached to the component 22. The computer has then storedidentification, position and orientation information relating to thefiducial for component 22 correlated with the data such as configurationand shape data for the item 22 so that upon registration, when sensor 16tracks the item 22 fiducial 14 in the infrared field, monitor 24 canshow the cutting block component 22 moving and turning, and properlypositioned and oriented relative to the body part which is also beingtracked. FIGS. 12-14 show similar registration for other instrumentationcomponents 22.

Registration of Anatomy and Constructs

Similarly, the mechanical axis and other axes or constructs of bodyparts 10 and 12 can also be “registered” for tracking by the system.Again, the system has employed a fluoroscope to obtain images of thefemoral head, knee and ankle of the sort shown in FIGS. 4-10. The systemcorrelates such images with the position and orientation of the C-armand the patient anatomy in real time as discussed above with the use offiducials 14 placed on the body parts before image acquisition and whichremain in position during the surgical procedure. Using these imagesand/or the probe, the surgeon can select and register in the computer 18the center of the femoral head and ankle in orthogonal views, usuallyanterior/posterior and lateral, on a touch screen. The surgeon uses theprobe to select any desired anatomical landmarks or references at theoperative site of the knee or on the skin or surgical draping over theskin, as on the ankle. These points are registered in three dimensionalspace by the system and are tracked relative to the fiducials on thepatient anatomy which are preferably placed intraoperatively. FIG. 15shows the surgeon using probe 26 to designate or register landmarks onthe condylar portion of femur 12 using probe 26 in order to feed to thecomputer 18 the position of one point needed to determine, store, anddisplay the epicondylar axis. (See FIG. 20 which shows the epicondylaraxis and the anterior-posterior plane and for lateral plane.) Althoughregistering points using actual bone structure such as in FIG. 15 is onepreferred way to establish the axis, a cloud of points approach by whichthe probe 26 is used to designate multiple points on the surface of thebone structure can be employed, as can moving the body part and trackingmovement to establish a center of rotation as discussed above. Once thecenter of rotation for the femoral head and the condylar component havebeen registered, the computer is able to calculate, store, and render,and otherwise use data for, the mechanical axis of the femur 12. FIG. 17once again shows the probe 26 being used to designate points on thecondylar component of the femur 12.

FIG. 18 shows the onscreen images being obtained when the surgeonregisters certain points on the bone surface using the probe 26 in orderto establish the femoral mechanical axis. The tibial mechanical axis isthen established by designating points to determine the centers of theproximal and distal ends of the tibia so that the mechanical axis can becalculated, stored, and subsequently used by the computer 18. FIG. 20shows designated points for determining the epicondylar axis, both inthe anterior/posterior and lateral planes while FIG. 21 shows suchdetermination of the anterior-posterior axis as rendered onscreen. Theposterior condylar axis is also determined by designating points or asotherwise desired, as rendered on the computer generated geometricimages overlain or displayed in combination with the fluoroscopicimages, all of which are keyed to fiducials 14 being tracked by sensors16.

FIG. 23 shows an adjustable circle graphic which can be generated andpresented in combination with orthogonal fluoroscopic images of thefemoral head, and tracked by the computer 18 when the surgeon moves iton screen in order to establish the centers of the femoral head in boththe anterior-posterior and lateral planes.

FIG. 24 is an onscreen image showing the anterior-posterior axis,epicondylar axis and posterior condylar axis from points which have beendesignated as described above. These constructs are generated by thecomputer 18 and presented on monitor 24 in combination with thefluoroscopic images of the femur 12, correctly positioned and orientedrelative thereto as tracked by the system. In the fluoroscopic/computergenerated image combination shown at left bottom of FIG. 24, a“sawbones” knee as shown in certain drawings above which contains radioopaque materials is represented fluoroscopically and tracked usingsensor 16 while the computer generates and displays the mechanical axisof the femur 12 which runs generally horizontally. The epicondylar axisruns generally vertically, and the anterior/posterior axis runsgenerally diagonally. The image at bottom right shows similarinformation in a lateral view. Here, the anterior-posterior axis runsgenerally horizontally while the epicondylar axis runs generallydiagonally, and the mechanical axis generally vertically.

FIG. 24, as is the case with a number of screen presentations generatedand presented by the system of FIGS. 4-39, also shows at center a listof landmarks to be registered in order to generate relevant axes andconstructs useful in navigation, positioning and assessment duringsurgery. Textural cues may also be presented which suggest to thesurgeon next steps in the process of registering landmarks andestablishing relevant axes. Such instructions may be generated as thecomputer 18 tracks, from one step to the next, registration of items 22and bone locations as well as other measures being taken by the surgeonduring the surgical operation.

FIG. 25 shows mechanical, lateral, anterior-posterior axes for the tibiaaccording to points are registered by the surgeon.

FIG. 26 is another onscreen image showing the axes for the femur 12.

Any desired axes or other constructs can be created, tracked anddisplayed, in order to model and generate images and data showing anydesired static or kinematic function of the knee for any purposesrelated to a UKA.

Modifying Bone

After the mechanical axis and other rotation axes and constructsrelating to the femur and tibia are established, instrumentation can beproperly oriented to resect or modify bone in order to fit trialcomponents and implant components properly according to the embodimentof the invention shown in FIGS. 4-39. Instrumentation such as, forinstance, cutting blocks, to which fiducials 14 are mounted, can beemployed. The system can then track instrumentation as the surgeonmanipulates it for optimum positioning. In other words, the surgeon can“navigate” the instrumentation for optimum positioning using the systemand the monitor. In this manner, instrumentation may be positionedaccording to the system of this embodiment in order to align theostetomies to the mechanical and rotational axes or reference axes on anextramedullary rod that does not violate the canal, on an intramedullaryrod, or on any other type of rod. The touchscreen 24 can then alsodisplay the instrument such as the cutting block and/or the implantrelative to the instrument and the rod during this process, in order,among other things, properly to select size of implant and perhapsimplant type. As the instrument moves, the varus/valgus,flexion/extension and internal/external rotation of the relativecomponent position can be calculated and shown with respect to thereferenced axes; in the preferred embodiment, this can be done at a rateof six cycles per second or faster. The instrument position is thenfixed in the computer and physically and the bone resections are made.

FIG. 27 shows orientation of an extramedullary rod to which a fiducial14 is attached via impactor 22. The surgeon views the screen 24 whichhas an image as shown in FIG. 29 of the rod overlain on or incombination with the femur 12 fluoroscopic image as the two are actuallypositioned and oriented relative to one another in space. The surgeonthen navigates the rod into place preferably along the mechanical axisof the femur and drives it home with appropriate mallet or other device.The present invention thus avoids the need to bore a hole in themetaphysis of the femur and place a reamer or other rod into themedullary canal which can cause fat embolism, hemorrhaging, infectionand other untoward and undesired effects.

FIG. 28 also shows the extramedullary rod being located. FIG. 29 showsfluoroscopic images, both anterior-posterior and lateral, with axes, andwith a computer generated and tracked image of the rod superposed or incombination with the fluoroscopic images of the femur and tibia. FIG. 30shows the rod superimposed on the femoral fluoroscopic image similar towhat is shown in FIG. 29.

FIG. 29 also shows other information relevant to the surgeon such as thename of the component being overlain on the femur image, suggestions orinstructions at the lower left, and angle of the rod in varus/valgus andextension relative to the axes. Any or all of this information can beused to navigate and position the rod relative to the femur. At a pointin time during or after placement of the rod, its tracking may be“handed off” from the impactor fiducial 14 to the femur fiducal 14 asdiscussed below.

Once the extramedullary rod, intramedullary rod, or any other type ofrod has been placed, instrumentation can be positioned as tracked inposition and orientation by sensor 16 and displayed on screen face 24.Thus, a cutting block of the sort used to establish the condylaranterior cut, with its fiducial 14 attached, is introduced into thefield and positioned on the rod. Because the cutting block correspondsto a particular implant product and can be adjusted and designated onscreen to correspond to a particular implant size of that product, thecomputer 18 can generate and display a graphic of the cutting block andthe femoral component overlain on the fluoroscopic image. The surgeoncan thus navigate and position the cutting block on screen using notonly images of the cutting block on the bone, but also images of thecorresponding femoral component which will be ultimately installed. Thesurgeon can thus adjust the positioning of the physical cutting blockcomponent, and secure it to the rod in order to resect the anterior ofthe condylar portion of the femur in order to optimally fit and positionthe ultimate femoral component being shown on the screen. Other cuttingblocks and other resections may be positioned and made similarly on thecondylar component.

In a similar fashion, instrumentation may be navigated and positioned onthe proximal portion of the tibia 10 and as tracked by sensor 16 and onscreen by images of the cutting block and the implant component.

FIGS. 33-37 show instrumentation being positioned relative to femur 12as tracked by the system for resection of the condylar component inorder to receive a particular size of implant component. Various cuttingblocks and their attached fiducials can be seen in these views.

Navigation, Placement and Assessment of Trials and Implants

Once resection and modification of bone has been accomplished, implanttrials can then be installed and tracked by the system in a mannersimilar to navigating and positioning the instrumentation, as displayedon the screen 24. Thus, a femoral component trial, a tibial plateautrial, and a bearing plate trial may be placed as navigated on screenusing computer generated overlays corresponding to the trials.

During the trial installation process, and also during the implantcomponent installation process, instrument positioning process or at anyother desired point in surgical or other operations according to thepresent invention, the system can transition or segue from tracking acomponent according to a first fiducial to tracking the componentaccording to a second fiducial. Thus, the trial femoral component ismounted on an impactor to which is attached a fiducial 14. The trialcomponent is installed and positioned using the impactor. The computer18 “knows” the position and orientation of the trial relative to thefiducial on the impactor (such as by prior registration of the componentattached to the impactor) so that it can generate and display the imageof the femoral component trial on screen 24 overlaid on the fluoroscopicimage of the condylar component. At any desired point in time, before,during or after the trial component is properly placed on the condylarcomponent of the femur to align with mechanical axis and according toproper orientation relative to other axes, the system can be instructedby foot pedal or otherwise to begin tracking the position of the trialcomponent using the fiducial attached to the femur rather than the oneattached to the impactor. According to the preferred embodiment, thesensor 16 “sees” at this point in time both the fiducials on theimpactor and the femur 12 so that it already “knows” the position andorientation of the trial component relative to the fiducial on theimpactor and is thus able to calculate and store for later use theposition and orientation of the trial component relative to the femur 12fiducial. Once this “handoff” happens, the impactor can be removed andthe trial component tracked with the femur fiducial 14 as part of ormoving in concert with the femur 12. Similar handoff procedures may beused in any other instance as desired in accordance with the presentinvention.

Alternatively, the tibial trial can be placed on the proximal tibia andthen registered using the probe 26. Probe 26 is used to designatepreferably at least three features on the tibial trial of knowncoordinates, such as bone spike holes. As the probe is placed onto eachfeature, the system is prompted to save that coordinate position so thatthe system can match the tibial trial's feature's coordinates to thesaved coordinates. The system then tracks the tibial trial relative tothe tibial anatomical reference frame.

Once the trial components are installed, the surgeon can assessalignment and stability of the components and the joint. During suchassessment, in trial reduction, the computer can display on monitor 24the relative motion between the trial components to allow the surgeon tomake soft tissue releases and changes in order to improve the kinematicsof the knee. The system can also apply rules and/or intelligence to makesuggestions based on the information such as what soft tissue releasesto make if the surgeon desires. The system can also display how the softtissue releases are to be made.

During this assessment, the surgeon may conduct certain assessmentprocesses such as external/internal rotation or rotary laxity testing,varus/valgus tests, and anterior-posterior drawer at 0 and 90 degreesand mid range. Thus, in the AP drawer test, the surgeon can position thetibia at the first location and press the foot pedal. He then positionsthe tibia at the second location and once again presses the foot pedalso that the computer has registered and stored two locations in order tocalculate and display the drawer and whether it is acceptable for thepatient and the product involved. If not, the computer can apply rulesin order to generate and display suggestions for releasing ligaments orother tissue, or using other component sizes or types. Once the propertissue releases have been made, if necessary, and alignment andstability are acceptable as noted quantitatively on screen about allaxes, the trial components may be removed and actual componentsnavigated, installed, and assessed in performance in a manner similar tothat in which the trial components were navigated, installed, andassessed.

At the end of the case, all alignment information can be saved for thepatient file. This is of great assistance to the surgeon due to the factthat the outcome of implant positioning can be seen before anyresectioning has been done on the bone. The system is also capable oftracking the patella and resulting placement of cutting guides and thepatellar trial position. The system then tracks alignment of the patellawith the patellar femoral groove and will give feedback on issues, suchas, patellar tilt.

The tracking and image information provided by systems and processesaccording to the present invention facilitate telemedical techniques,because they provide useful images for distribution to distantgeographic locations where expert surgical or medical specialists maycollaborate during surgery. Thus, systems and processes according to thepresent invention can be used in connection with computing functionality18 which is networked or otherwise in communication with computingfunctionality in other locations, whether by PSTN, information exchangeinfrastructures such as packet switched networks including the Internet,or as otherwise desire. Such remote imaging may occur on computers,wireless devices, videoconferencing devices or in any other mode or onany other platform which is now or may in the future be capable ofrending images or parts of them produced in accordance with the presentinvention. Parallel communication links such as switched or unswitchedtelephone call connections may also accompany or form part of suchtelemedical techniques. Distant databases such as online catalogs ofimplant suppliers or prosthetics buyers or distributors may form part ofor be networked with functionality 18 to give the surgeon in real timeaccess to additional options for implants which could be procured andused during the surgical operation.

What is claimed is:
 1. A process for performing unicompartmental kneearthroplasty surgical operations on portions of a knee joint comprising:(a) obtaining data corresponding to the structure of a body part forminga portion of said joint with a locator, wherein the body part and thelocator are each attached to a fiducial capable of being tracked by atleast one position sensor; (b) registering a unicompartmental kneearthroplasty trial component attached at least indirectly to a fiducialcapable of being tracked by at least one position sensor; (c) using acomputer which receives signals from the at least one sensor, trackingposition and orientation of the trial component relative to the bodypart; and (d) generating and displaying on a monitor associated with thecomputer a visual image of the trial component properly positioned andoriented relative to the body part.
 2. A process for performingunicompartmental knee arthroplasty surgical operations on portions of aknee joint, comprising: (a) obtaining data corresponding to structure ofa body part forming a portion of said joint with a locator, wherein thebody part and the locator are each attached to a fiducial capable ofbeing tracked by at least one position sensor; (b) registering aunicompartmental knee arthroplasty surgical instrument attached to afiducial capable of being tracked by at least one position sensor; (c)using a computer which receives signals from the at least one sensor,tracking position and orientation of the surgical instrument relative tothe body part; (d) generating and displaying on a monitor associatedwith the computer a visual image of the instrument properly positionedand oriented relative to the body part; (e) navigating the instrumentrelative to the body part and attaching the instrument to the body partaccording to the image; and (f) modifying the body part using theinstrument attached to the body part; and (g) assessing performance ofthe joint using images displayed on said monitor.
 3. The process ofclaim 2, further comprising registering a body part by intraoperativelydesignating at least one point on the body part with a probe, whereinthe probe is attached to a fiducial capable of being tracked by said atleast one position sensor.
 4. The process of claim 2, wherein the bodypart comprises one of a femur, a tibia, and a patella.
 5. The process ofclaim 2, wherein the locator comprises one of a C-arm fluoroscope, a CTscanner, MRI equipment, ultrasound equipment, laser scanning equipmentand a probe.
 6. The process of claim 2, wherein the fiducials compriseone of active fiducials, passive fiducials and hybrid active/passivefiducials.
 7. The process of claim 2, wherein the position trackingsensors comprise one of infrared sensors, electromagnetic sensors,electrostatic sensors, light sensors, sound sensors, and radiofrequencysensors.
 8. The process of claim 2, wherein the surgical instrumentcomprises a rod and a cutting block.
 9. A process for performingunicompartmental knee arthroplasty surgical operations on portions of aknee joint comprising: (a) obtaining data corresponding to structure ofa body part forming a portion of said joint with a locator, wherein thebody part and the locator are each attached to a fiducial capable ofbeing tracked by at least one position sensor; (b) registering aunicompartmental knee arthroplasty surgical instrument attached to afiducial capable of being tracked by at least one position sensor; (c)using a computer which receives signals from the at least one sensor,tracking position and orientation of the instrument relative to the bodypart; (d) generating and displaying on a monitor associated with thecomputer a visual image of the instrument properly positioned andoriented relative to the body part; (e) navigating the instrumentrelative to the body part and attaching the instrument to the body partaccording to the image; (f) modifying the body part using the instrumentattached to the body part; (g) removing the instrument from the bodypart; (h) registering a unicompartmental knee arthroplasty trialcomponent attached to a fiducial capable of being tracked by at leastone position sensor; (i) tracking position and orientation of the trialcomponent relative to the body part; (j) generating and displaying onthe monitor a visual image of the trial component properly positionedand oriented relative to the body part; (k) navigating and installingthe trial component on the body part according to the image; and (I)assessing performance of the knee joint using images displayed on themonitor.
 10. The process of claim 9, further comprising: (a)discontinuing tracking of the trial component using the fiducialattached to the trial component; and (b) initiating tracking of thetrial component using the fiducial attached to the body part on whichthe trial component is installed.
 11. The process of claim 9, whereinthe body part comprises one of a femur, a tibia and a patella.
 12. Theprocess of claim 9, wherein the locator comprises one of a C-armfluoroscope, a CT scanner, MRI equipment, ultrasound equipment, laserscanning equipment and a probe.
 13. The process of claim 9, wherein thefiducials comprise one of active fiducials, passive fiducials, andhybrid active/passive fiducials.
 14. The process of claim 9, wherein theposition/orientation tracking sensors comprise at least one of infraredsensors, electromagnetic sensors, electrostatic sensors, light sensors,sound sensors, and radiofrequency sensors.
 15. The process of claim 9,wherein the trial component comprises a femoral component.
 16. Theprocess of claim 9, further comprising: (a) performing soft tissuebalancing tests while the computer continues to track the fiducials; (b)using data generated by the computer, including information related toat least one of release points and amounts, to assess alignment andstability of the trial component and the knee joint; and (c) releasingsoft tissue to adjust alignment and stability of the knee joint.
 17. Aprocess for performing unicompartmental knee arthroplasty surgicaloperations on portions of a knee joint comprising: (a) obtaining datacorresponding to structure of a body part forming a portion of saidjoint with a locator, wherein the body part and the locator are eachattached to a fiducial capable of being tracked by at least one positionsensor; (b) registering a unicompartmental knee arthroplasty implanttrial component attached at least indirectly to a fiducial capable ofbeing tracked by at least one position sensor; (c) using a computerwhich receives signals from the at least one sensor, tracking positionand orientation of the trial component relative to the body part; (d)generating and displaying on a monitor associated with the computer avisual image of the trial component properly positioned and orientedrelative to the body part; (e) navigating the trial component relativeto the body part and attaching the trial component to the body partaccording to the image; (f) performing soft tissue balancing tests whilethe computer continues to track the fiducials; (g) using data generatedby the computer to assess alignment and stability of the joint with thetrial component attached; and (h) releasing soft tissue to adjustalignment and stability.
 18. A process for performing unicompmaratmentalknee arthroplasty surgical operations on portions of a knee jointcomprising: (a) obtaining data corresponding to structure of a body partforming a portion of said joint with a locator, wherein the body partand the locator are each attached to a fiducial capable of being trackedby at least one position sensor; (b) registering a unicompmaratmentalknee arthroplasty implant component attached at least indirectly to afiducial capable of being tracked by at least one position sensor; (c)using a computer which receives signals from the at least one positionsensor, tracking position and orientation of the implant componentrelative to the body part; (d) generating and displaying on a monitorassociated with the computer a visual image of the implant componentproperly positioned and oriented relative to the knee joint; and (e)navigating the implant component relative to the body part and attachingthe implant component to the body part according to the image.
 19. Theprocess of claim 18, further comprising performing soft tissue balancingtests on the joint with implant component installed while the computercontinues to track the fiducials.
 20. A process for performingunicompartmental knee arthroplasty surgical operations on portion of aknee joint comprising: (a) obtaining data corresponding to structure ofa body part forming a portion of said joint with a locator, wherein thebody part and the locator are each attached to a fiducial capable ofbeing tracked by at least one position sensor; (b) registering aunicompartmental knee arthroplasty implant component attached to a toolto which is attached a fiducial capable of being tracked by at least oneposition sensor; (c) using a computer which receives signals from the atleast one sensor, tracking position and orientation of the implantcomponent relative to the body part; (d) generating and displaying on amonitor associated with the computer a visual image of the implantcomponent properly positioned and oriented relative to the body part;(e) navigating the implant component relative to the body part andattaching the implant component to the body part according to the image;(f) discontinuing tracking of the implant component using the fiducialattached to the tool; (g) initiating tracking of the implant componentusing the fiducial attached to the body part on which the implantcomponent is attached; (h) performing soft tissue balancing tests whilethe computer continues to track the fiducials; and (i) using datagenerated by the computer to assess alignment and stability of the jointwith the implant installed.